Method of softening water



Nov. 16, 1937.

M /0 Gaiam I Patented Nov. 16, 1937 1;

i umipsmm Y 2,099,287Vv PATE Nr orifice This invention relates to methods ofsoften-v ing water. n

' l0 Y tain mineral substances, such aszeolites.

It is well known that somev so-called hard waters v,are unsuited for general use because of the presence therein of lsalts of such minerals as calcium and'` magnesium, and` that these Waters may be made ysuitable for such use, or softened, by the removal of said hardening salts. It is also welly known that this may ,beaccomplished by passing the hard Water through cer- In recent years, thebusiness of softening-Water'and of' providing apparatusV therefor, has become of considerable commercial importance.

In the apparatus generally employed thereV is a tank, which maybe considered a lter, andV ,'Which may be either open or closed at itstop. Within the lower part of this tank is a bed of gravel v'which supports a mass of zeolites., i These zeolites, having. rst .been activated by treatment with a solution of common Asalt (sodium chloride), and thus charged with sodium, are-in condition to exchange their sodium content forithefcalcium and magnesium content of the hard4 water; and when the latter is "passed or filtered through them this base Vexchange Vtakes :place andthe hard Water is softened. This exchange rapidly depletes the sodiuinrcharge of the Zeolites and loads the latter with the calcium and magnesium salts, withthe result thatthe Zeolites lose their ting 01T the flow of the hard vwaterand in then passing a strong solution of sodium Vchloride through the zeolites, either in the same direction reverse direction. f

A strong solutiony of sodium chloridei is necessary for regeneration of the zeolites for the `reason that the normal reaction of :the zeolites is'to pick up calcium and magnesium and to pass off 'sodium'. InV order to reverse this exchange, an excessof sodium chloride mustfbe present, the normal amount required being substantially 3400 grains VV(1/2 pound) per Veach 1000 grains of hardness in` terms of "calcium carbonate to be removed from the water. This means that approximately three units perweight of regenerating salt have been used for the removal of `.one

as the previous flow of the hard ywater or in the Y unit perl weightV of the hardening salts. "Thus,

much more sodium chloride has been usedto effect complete regeneration than is actually necessary, as'. will hereinafter 'be/shown. V

One object of `my invention Yist@ reduce the amountof sodium chloride employed by recovering a portion kof the brine which has-been passed through the zeolites. This recovered brine is passedthroughthezeolites vas the first brine in the nextv regeneration; Having then been twice, used in regeneration', it isgenerally so'rcontaminated with the hardeningsalts as to g be unfit for further use, and so is allowed frto 1 waste. After the zeoliteslfiaye been treated with this brine .which hasbeen recovered from the previous regeneration; they 'are giveni a short fresh-Water wash to carry away thevexcess calf ciumand magnesium which have been freed,l by the sodium of the brinebutwhich remain in the zeolites; ThenV the latter, are`v further: ree

generated by passing through them arpure or fresh sodium-chloridesolution. The main por-v tion of Ythis brine which isused afterthe Yshort fresh-water rinse is vthe partwhich is recovered for use in the first step ofthesucceeding regen-` eration. The complete regeneration comprises, therefore, first, the `useof this recovered brine; second, the short, fresh-water. wash, and, third, the pure sodium-chloride brine, which is recovered for use inthe first step ofthe succeeding regeneration. VTlfiisrecovered brine isnotcontaminated with an excess .amount of calcium and magnesium and is, therefore, suitable for use once more, but inthe first part-ef the succeeding regeneration, asstated. By means of a saltY 'water` hydrometer, the` specific gravity ofthe liquid passing fromthe -filterf may be tested to determine when the contaminated brine has passed out of the zeolites. to waste and alsoto determine whenfthe fresh brineV has passed through theV zeolitesk and is in condition forrecovery. Y V

VIn the early practiceof water-softening-the particles of the `softening material werev relatively coarse, .,being of approximately the size oi. buckshot. were left betweenthe particles, Vand the total surface exposed for actioni upon thewater was correspondingly limited. Consequently, the softening action was slow, as was also'. the regeneration. In' those days it Wasconsidered advisable,

Relatively large voids oninterstices if not absolutely necessary, to flow the brinej in the reverse direction fromY that vof the flow ofthe hard water. Then the size of the'. particles Vof the softening materials was much reduced, until they now average little if any' greater than the head of an ordinary pin. This has had' the effect 'of compacting the mass, largely `filling' ,upithe voids and greatly .increasing thetotal: active sur-.- 'face of' the materials. Asa result, bothzthe softening and regenerating operations are greatly accelerated, it now requiring but from two and a half to three hours to accomplish what previously had required from eight to ten hours. As a further result and due to the denser bed of the softening materials, the water and brine, assuming the same pressure as before, percolate through more slowly and it has become practical to pass both of them through in the same direction, which is. the practice I now prefer.

At the'beginning of a run of hard water, the zeolites, having been activated or regenerated,

those particles which first contact the water give up their sodium content and take up the calcium and magnesium content of the water, becoming thus contaminated. This contaminating action proceeds progressively more` and more deeply intoV the bed of zeolites until finally regeneration has become necessary. In the same way, the regenerating brne first acts upon the particles which it first contacts which,in case it be flowed in the same direction as the hard water, are the same particles as were first contaminated' in the softening operation. The brine acts progressively more and more deeply into the bed until finally all the particles have freedtheir hardening content. However, not all of the hardening salts have been washed out at the time the base exchange has been completed. This could be effected by continuing the flow of the brine, as is the usual practice; but that would result-in a seriousfwaste-o'f brine and of th-e sodium chloride it contains, sincel al1 of this part of the brine is wasted'. It can be accomplished just aswell by fresh water; and forthat reason and to effect that saving, I give the zeolites the fresh-water wash after the recovered'brine has been passed therethrough and before the fresh and pure brine is applied.

At the time the fresh-water wash isintroduced, thereforathe actual regeneration is almost complete, although substantial amounts of the hardening salts remain in the bed to be carried out by the fresh water. This means thatv the regenerationhas been mostly effected by the use of the recovered brine; and that means that the said recovered brinepossesses the strength necessary to accomplish that result. Asa matter of fact, the fresh,'pure brine takes' up such a small amount ofthe hardening salts and gives up so little of its sodium chloride in exchange thatit is but slightly contaminated and is almost as strong as it was before it contacted with the zeolites. That is to say, the recovered brine has almost thesame strength as the fresh, pure brine and is almost of the same purity. It is important that the regenerative power of the recovered brine be nearly the same as the regenerative power ofthe fresh brine, since it must have sufficient sodium chloride in it to carry through the entire bed of zeolitesy and' effect the base exchange, as hereinbefore described. As will be seen, therefore, I' eiect a saving of'salt by the recovery of the brine after the fresh-water and also by the use of the fresh-water wash which carries away the freed but lingering particles of the hardening salts.

In softening water,` the normal action is for the Zeoli'tes to raise the pH value of the water slightly, so thatA the softened water carries a higher pH value than the hard water. As is well understood, a liquid whichlisperfectly neutral, such as chemically pure distilledr water, has a pH value of 7. If it `has a' lower pH value, it is acid, whereas ifits pH' value is greater than '7,' it is alkaline. To

be efficient as a regenerating agent, the brine must be alkaline and should have a pH value somewhere above '7.V I have found a value of 7.4 to give very satisfactory results.

Some waters are naturally alkaline, and if they be used in making up the brine, special treatment may not be necessary to maintain the pl-I value of the brine sufficiently high. When, however, the brine water is acid, something must be done to raise its pH value, else the softening operation will be inefficient. Therefore, one of the objects of my invention is to insure the efficiency of a water-softening system by seeing to it that the brine used for regenerating the zeolites is alkaline. This object is preferably attainedy by aeration; and, as will hereinafter be more fully set forth, I prefer to aerate both the water which is to be used in making up the brine in the first instance and, later, to aerate that part of the brine which has been recovered for the next regeneration.

To improve the alkalinity, or to raise the pH Value, ofa brine'something must be done to the water, since the sodium chloride is a neutral salt and will not affect either the acidity or the alkalinity of the solution. The use of chemical means for increasing the pH value of the recoveredbrine, which always carries some calcium and magnesium chlorides, is not practicable because the chemicals employed either precipitate the calcium and magnesium or increase the hardness of the'recovered brine, depending on the chemical used; and, in either case, a brine thus treated would be unsuited for use in the softener. Then, the addition of any strong alkali Vto the brine which would remain even as a trace in the zeolites and later be passed out with the softened water, would be objectionable for many uses and in many cases prohibitive. If the softened water be used for drinking purposes, for example, the presence therein of some alkalis would be objectionable from the standpoint of health. Moreover, many municipalities now soften their entire water. supply, and the means employed for raising the pH value of the regenerating brine must be inexpensive Vin its installation, maintenance and operation.

According to the modern theory of electrolytic dissociation, all liquids of which water is a constituent .contain free H and OH ions. IfV the H u ions predominate, the liquid is acid and if the OH ionspredominate the liquid is alkaline. If, therefore, the water which is used in making up the brine for regenerating the zeolites contains an excess of free H ions, or if it fails to contain a predominating amount of the OH ions, it is undesirable for use in making up the brine and its use in a softening system would gradually result in rendering the latter inefficient if, indeed, it would not render it practically inoperative.

As stated, the normal action in softening water is for the zeolites to raise the pH value of the water slightly, so that the softened water carries a higher pH value than the hard water. At the same time, a slight hydrogen ion concentration takes place in thezeoltes, which is neutralized at the time of regeneration. After the brine has passed through therzeolites the pH value of the recoverable brine is usually on the acid side, or nearly so, depending upon the alkalinity of the brine when rst prepared. If this recoverable brine be again introduced into the zeolites without first raising its pH value to or above r',the hydrogen ion concentration in the Zeolites will not be sufficiently neutralized but it will increase caf 'a1/valvev 23a, which is automatically controlled i land will cause* the 'if'. eol-itesV- gradually to` lose their o by a oat 24 within the receptacle 20 and by f efliciency. AAeration is the preferred'method for .increasing thepH value o-f the recoveredbrine to 'lI or above. VThis Vmay be, and preferably is' `n most cases, accomplishedbycausing there- "covered brine, or the V'water rwhich is tobe used 1 in making `up the brine, to pass in thin (sheets or "in fine'streams-or infajspray-throughiair so that the oxygen in'theair may contact witheveryV In'fsome.

l'receptacle 201are preferably located directly above the brine-tanky l, as shown, they may be placed small particle' of the brine or Vwater. o cases where compressed air, or oxygenor.- ozone or some gas' which contains freefoxygen is available, itmay'be used Vin'rais'ing thepHgvalueof `the brine or water; Asjwill `be seen, I'prefer to'r aerate the water Vwhich isused inthe -fresh- Ywater wash after regeneration with the recovered brine.

The method of water softening above set forth may be carried out by the use of apparatus which may be varied in details in diiferent'plants.

The` accompanying drawing shows a suitable apparatus and the one which is, at present, preferred. Howevenit is to be understood that the accompanying claims are not intended to be limited to thedetails shownany further than their v'specific terms require.'r Whilerbut a single unit of apparatus is shown, it will be understood that aplant mayrequire a'multiple of such ory similar units',`and.-thatv V,such a plant is within the scope of my invention; Y Y

In the drawing`,'li"ig.` 1 is a diagrammatic view rof an apparatus suitablefor carrying out my invention and Fig.' 2 is av plan viewfof a modified -fform of aerating device, the same being adapted for use of compressed air or oxygen or ozone.

The water which is tobe softened is introduced through the pipe Y5, which is branched at 6, one branch, y'1, leading, through a valve 8, l Ypipe 9 and suitable fittings, to the inlet l0 of 40 the tank or' lter lll. This filter may be of any suitable form and construction, but it is preferably cylindrical with closed ends, as indicated.

Within'the lter, atfthe lower part thereof, is a bed oi gravel upon which the zeolites are Asupported. The specific nature of the filter and of its contents form nopart of my present invention, and fuller description and illustration thereof is deemed unnecessary. The water to be softened passes downwardly through thelter from the inlet Ill to the bottom andout through a suitable /outlet l2. Thence it passes upwardly Vtl'irougl'i pipes i3 and I4 and valve rI5 to the outthere is normally maintained a quantity of undissolved salt (sodiumchloride). Howeveiythe `apparatus isv adaptedv to the batch method'als'o,

in which onlyA such "a quantity of salt is-,placed -in thetank I9v as will be fully dissolvedby thel i water thereinvor passing therethrough. Above the brine-tank is `a receptacle 2l! and above it, is an aerator 2l of any suitable'type. From the `point 6 inA the water pipe`5, another branch pipe,

22, leads upwardly and extends over the aerator 2l in position to deliver water-thereto. The pipe 22 is provided with a shut-01T valve 23 and with vwaste pipe 4l?.

means of whichthe water inthe receptacle may be retained at `adesired level. As will be understoodfthe water from the pipe 22 is causedto flow downwardly by gravity through the aerator and is broken'up intosmall particlesso as.l to be .thoroughlyexposed tothe air. This is'rforj the' purpose of raisingthe pH value of vthewater, Vas has been explained. While the aerator 2l and its elsewhere so longas-.they'are at a higher level than said tank. `Of coursefthey may be placed at 'the same level as, orfeven lower than, the brine-tank and the water pumped into the latter, but I much prefer the gravity -flow and the arrangement shown. The receptacle 2)` is connected with the brine-tank through pipes 25 and .26, the latter pipe entering the tank and having a float-controlled valve 2l to shut off the water yautomatically when the desired amount has entered the tank. The pipe 26 is furtherfprovided ywith a v"manually controlled valve 21a for shutthe pipes 9` and 3D. The structure of this ejec-Y tor, which is of-a conventional type, isindioated ink dotted lines, and the same is operatedby a jet of steam, as will be understood. Obviously, the brine vcould be forced into the filterby a pump if preferred. The steam is suppliedV from a pipe 33 having a branch 34 with-a control valve 35. through a pipe'SB having a valve 3l therein, for a-purpose hereinafter explained.

Before vthe first brine is introducedLV at -the beginning of?V the regenerating operation, the valves 8 land I5 are closed to shut off the water from the pipe 5. Then a valve 38 in apipe 39 is opened, which pipe is connected with the pipe I3 from the outlet l2 ofthe 'filter vand with Aa 39,v valve 3S and waste-pipe 4Q to a sewer or sump. The fresh-water wash is the nextstep in order, and the water for that purpose comes fromv the receptacle 2B of the aerator 2l. To this end, the valve 28a;is closed and the valves 3| and 35 Vare opened, the latter admitting steam to the ejector to force'the aerated water through the filter.V At the saine time, Vthe valve 23 is preferably -open to furnish all the waterV needed for the fresh-water wash and to rell the receptacle to its normal level. The water passing through The Apipes 25 and Eil-are connected The brine first used, which is that recovered from theV previous regeneration, is thus allowed to pass through Vthe pipes i3 and The pipe 23 isprovided with a the `lter washes-out the freed but lingering parts H of the-'hardening salts, carries thernwto'wasteH through thepipes I3, 3Q, and to, and, at the same time, lls the lter'tank. Having first been aerated, this waterfhas a relatively high pH' value and is thus in condition to assist in Vovercoming any acid condition in the filter. When, by hydrometer test, it is determined that the'waste water passing through the pipe 4t carries 'substantially none of the hardening salts, the time Yfrom the lower part ofthe tank where the brine is naturally strongest and nearly or quite saturated. It may be desired to weaken this brine somewhat, and this can be done and nicely controlled'by opening more or less the Valve 31. Then, when the steam is turned on at valve 35 and the valve 3l is opened, the lbrine in the tank I9 is drawn outis forced into the filter, displacing the aerated water therein and forcing it to the Waste pipe. If the brine be stronger than necessary, it may be cut in strength by permitting some aerated Water to pass through the valve V3l, thus to dilute the brine.

vWhen the hydrometer tests sho-w that the fresh brine has substantially displaced the wash water and hasthe proper specific gravity, the brine is vin condition for recovery for the next regeneration. The valve 35 is accordingly closed and a valve 4I in a pipe 42 is opened. This pipe connects with the outlet I2 and leads to the top of Van aerator 43 which, as shown, is preferably placed directly over the tank 44 for the recovered brine. This aerator may be of the same structure Aas'the aerator 2|, but it preferably discharges'directly into the tank 44.

As stated, the brine recovered in the tank 44 is used at the beginning of the next regeneration. It is drawn out through a pipe '45 by means of Yan ejector 46 which is supplied with steam from the pipe 33'through a valve'4`l, and is forced to the inlet=l of the filter through a pipe 48 which is provided with'a shut-off valve `49.

By using ejectors operated 'by steam, I am enabledto propel the brines without materially diluting them, as would be an objectionable result in some cases if water ejectors Were used. As stated, however, force pumps may be employed in place of the ejectors. Y

The operation may be summarized as follows: Assuming that the 4zeolites have been activated or regenerated, the valves 8 and I5 are opened to admit the Water to the filter at the inlet IS) and to permit it to now outwardly 4through the pipes I3, I4 and I6 to the places vfor use. The zeolites collect-the calcium and magnesium in thevvater yand give off their sodium, thus becoming exhausted of their sodium content and -charged 'withcalcium and magnesium. They now require regeneration, and this is effected by the brines from the tanks 44 'and I9. The brine in the tank 44, which has been recovered as described, is kfirst employed. Then the aerated fresh water from the receptacle 20 is sent through thefilter to remove the lingering traces of freed hardening salts and to improve the pI-I value of the contents of the filter, and then the fresh and pure brine from the tank I9 is employed and the main part thereof is recovered in the tank 44 for the next regeneration, the recovered brine having been aerated and its pH value raised by the aerator 43. When the operation of brining and the regeneration is complete, the zeolites Y'are in condition for softening the hard water from therpipe 5. The softening of -the Water again `contaminates the zeolites and necessitates ia furthe-r regeneration, so that the steps set forthfarerepeated indefinitely. As will be under.- stood, the first part of the softened water must be wasted since -itwill be mixed with the brine which it forces from the lter.

The apparatus is sometimes installed in places where there is .a supply of air under pressure. Inthese installations it is practicable to aerate the brine in *the tank 44 withthis compressed air, and Athis airmay also beused for aerating the water for making up the brine in the tank I9. In Fig. 2, I have shown a brine tank 44a,

corresponding to the tank 44,V to which an air Vpipe 50 is attached, said pipeleading to the central axis of the Vtank where it is branched, as shown at 50a; The branch pipes within the tank 1- are perforated to permit the air to bubble up through the'brine, thusto aerate it.

I claim: Y

1.7In the art of water softening in which successive runs of hard water .through zeolites are alternated with regenerations of said Zeolites,the method of regeneration which comprises passing a sodium chloride solution of one strengththrough the zeolites until the greater part of the hardening substances extracted from the Water has been'set free, then Washing .said zeolites lwith fresh-water until the effluent Water from the Zeolites contains substantially none of the -said freed Vhardening substances, then completingY the regeneration by the application of a second sodium chloride solution, the fresh water wash thus vserving effectually to separate-the two regenerating -solutions and to prevent theirintermingling, recovering apart of the last+mentioned solution and raising its pH value by aeration to prepare'it YforV usev as the rstregenerating solution in a succeeding regeneration. v

2. The method asset forth in claim 1 in which the second solution is a brine comprising, sodium chloride dissolved in aeratedwater.

3. The method vas set forth in claim 1 in which the fresh Water used for washing'the Zeolites is aerated before such use.

4. The method as set forth inclaim 1 in which the water used in making up the second solution referred to, the water used in the fresh water Y wash and the recovered regenerating solutionare all aerated beforethey are Y,passed through the zeolites.y

5. lIn the art of water softening in which successive runs of hardV water through zeolites are alternated With regenerations of said zeolites by bringing a sodium chloride regenerating-solution into intimate contact with the zeolites whereby a base exchange is effected and the pI-I value of said solution is lowered, lrecovering a portion of said solution, aerating such recovered` portion to raiseits pH value and thus further use in a subsequent regeneration.

6. In the regeneration of zeolites, the process comprising recovering and storing a salt solution which has been used in the later stages of an earlier regeneration, aerating said solution, running the aerated stored recovered salt solution through the exhausted zeolites to partially recondition the Zeolites, and subsequently passing a further quantity of salt solution through the'zeolites to complete their regeneration.

7. In the regeneration of zeolites, the process comprising recovering and storing a salt solution which has beenused in the later stages of an earlier regeneration, rst *aeratingY and then run- .ningthe aerated-stored recovered salt solution CERTIFICATE oF coRREcTioN, 'Patent No. 2,o99;287. November 16, 5195"(u CLAYTON W. WOODS'.

It is hereby certified that error appears in 'the' printed spe cif icat'ion of the above numbered patent requiring correction 4as follows: Page )4, second v column, line 5l, claim 5', after the word "thus" insert fit it for; and that the said Letters Patent should be read with this correction therein that the 'same may conform to the record of the oase in the Patent Office'.

signed andssealed this luth day of June Af: D., 1958.

Henry Van Arsdale (Seal) l Aeting Commissioner of Patents-.- 

